Sealed Quartz Tube Research Articles

Sur quelques aspects du transport en phase vapeur du sesquioxyde de vanadium V 2O 3 pur et dopé au chrome

Single crystals of pure or chromium-doped V 2O 3 are obtained by a TeCl 4 chemical transport method in sealed quartz tubes. The conditions of transport have been precised. For pure V 2O 3 the decrease in resistivity with increasing temperature is of an order of magnitude of 10 10 at the transition. An investigation by electron microscopy confirms the low temperature transition in single crystals of V 2O 3 and (V 1− x Cr x ) 2O 3.

Two modifications of cobalt dipotassium tetrachloride

High-temperature K2COC14: orthorhombic, a=26.838 (3), b=12.406 (1), c=7.262 (1 )~ , space group Pna21, Z = 1 2 , adopts a slightly modified fl-KzSO4 structure. Low-temperature K2COC14: monoclinic, a=6.801 (1), b=9.569 (1), c=12.757 (1)/~,, ,8=107.0 (1) °, space group P21/c, Z = 4 , adopts a strongly distorted ,8-K2SO4 structure. Introduction. The structure determination of KzCoC14 is part of an investigation of structural relationships and magnetic properties of ternary halides AxByXz with A an alkali metal, B a first-row transition element or an alkaline-earth metal and X = C1, Br or I. The phase diagram of the system KCI-CoCIz was constructed by Seifert (1961). Apart from K2COC14 (m.p. 436°C) it shows another compound, KCoC13, but not the phase transition we observe for K2CoCI 4. By melting stoichiometric amounts of KC1 and CoClz in an evacuated quartz tube and annealing the mixture at 400°C for one week, the orthorhombic modification of KzCoCI4 is obtained. After a few months this phase changes at room temperature into the monoclinic modification. The former is again obtained after annealing the latter at 400°C. The two phases are easily recognized by their X-ray powder diagrams. We were unable to measure the transition temperature by means of DTA, but visual inspection of samples after heating suggests a phase transition between 350 and 360°C. Lamotte & Vermeire (1975) report that powder diffractograms of K2COC14 and (NHa)zZnCI 4 can be indexed on the basis of an orthorhombic cell with axes a=8.90, b=12.39 and c=7.25 (.~) for KzCoCI4 and a=9.20, b = 12.56 and c=7.17 (•) for (NH4)2ZnCI 4. In both cases our diagrams show powder lines between d=3.47 and 3.51 A, which cannot be indexed with these cell parameters. On tripling the a parameter these reflexions can be indexed as 202, 231 and 112. Klug & Sears (1945) also report a tripled a parameter for KzZnCI4, based on single-crystal measurements. Dry KCI was obtained by heating in vacuo at 400 °C, and dry COC12 by heating COC12.6HzO in a stream of dry HCI gas at 400°C. Lowand high-temperature KzCoCI4 were obtained by melting a stoichiometric mixture of KCI and CoCIz in an evacuated sealed quartz tube and slowly lowering the temperature over the course of a few days to room temperature with a temperature gradient of about 50°C, with the higher temperature at the top of the melt. All manipulations of KzCoCI 4 were carried out in a glovebox filled with dry N2 or under dry paraffin oil. The crystallized blue material was broken into pieces and crystals were selected. A series of Weissenberg photographs showed some crystals with orthorhombic and some with monoclinic symmetry. One suitable crystal of each phase was collected and measured by means of an Enraf-Nonius three-circle single-crystal diffractometer. Intensities were recorded by the 0-20 scan method for all reflexions with 0 between 3 and 30 °. Monochromatic (graphite) Mo K0~ radiation was used for measuring the intensities. Background inteni ° sities were determined at 0+~zl , with z1=0.7+1.3 tan 0 °. The mean counting time was 25 s for each background and 50 s for the scan. Standard deviations were calculated from counting statistics. Absorption corrections were applied with a computer program written by de Graaff (1973), and new standard deviations (av) were calculated taking into account the inaccuracy of the absorption correction and attenuation factors of the filters used. Non-equivalent significant reflexions were reduced to F values and Wilson plots were calculated, yielding approximate values for the scale factors and overall isotropic temperature parameters, B. Table 1 gives the crystal and diffraction data. According to the reflexion conditions for orthorhombic KzCoCI4, another space group (Pnam) is possible, which the Patterson synthesis proved to be incorrect. Table 1. Crystal and diffraction data for K2CoCI 4

Contribution of thermodynamics to the investigation of the chemical transport of ferrous sulfide

The equilibrium compositions of the chemical systems Fe−S−X (X≡I2, Cl2) are computed as a function of the initial concentration of X, at P = 1 atm and T as a variable parameter. Large changes in these compositions versus n0X are predicted, as well as the competing occurrence of liquid and gaseous halides, thus bringing about a poor control of the gaseous transport rate. In addition, I2 is exhibiting a low chemical conversion, and is not well suited to such a transport reaction. Finally, the solid phase in equilibrium with a gas containing variable amounts of Fe(II) and Fe(III), must be off-stoichiometry. The experiments in sealed quartz tubes bear out quite well these predictions, though the actual situation is even more complicated with I2 due to the use of non-stoichiometric charges to avoid the quartz corrosion. The calculations with X≡HCl point out a simpler result, since both Fe(III) and liquid phases are excluded. Unfortunately the transport rate is also low according to the small change of Kp with T. Experiments agree well with these results, the small crystals having a nearly stoichiometric composition.

The morphology of Zn 3P 2 single crystals grown from the vapour phase

The morphology of Zn 3P 2 single crystals, grown from the vapour phase by sublimation of bulk Zn 3P 2 in a sealed quartz tube pulled through a high temperature gradient, has been investigated. X-ray diffraction examination showed that the main direction of crystal growth with a tetragonal unit cell is the [021] direction which corresponds to the [111] direction in the pseudocubic system. Transverse and longitudinal cross sections of the single crystals were mechanically polished and chemically etched. Optical examination of the cross sections indicated that the growth of Zn 3P 2 begins most frequently in the (011) plane. Striae which appeared in a cross section after chemical etching are attributed to the existence of strain fields generated in the sample as a result of temperature fluctuations or as a result of crystal structure defects in the core region.

The growth of large Cd 3P 2 crystals

Single crystals of Cd 3P 2 up to 45 mm in length and about 20 mm in diameter were grown from the vapour phase by pulling a sealed quartz tube through the temperature gradient.

On the miscibility gap of spinels Mn xFe 3− xO 4+γ

Annealing experiments at 940±5°C on Mn x Fe 3− x O 4+γ system were carried out in order to determine the equilibrium miscibility limits. The samples were annealed for 200 hr in sealed quartz tubes and quenched. Coexisting phases and relevant parameters were determined by X-ray diffraction. The immiscibility interval at the annealing temperature has been found by converting the c a ratios to corresponding x-values to be x cub = 2.54±0.03, x tetr = 2.73±0.03. The experiments concerning the possible influence of the oxygen content are also reported. A corrected version of the phase diagram based on the results obtained as well as on the critically selected data published previously by other authors had been suggested and discussed on the basis of a simple model.

Thermoluminescence study of radiation-induced defects in alkaline earth sulfates

Since these processes can be accompanied by thermoluminescen ce, we have carried out a study of the thermoluminescen ce (TL) curves of alkaline earth sulfates in both the unactivated and activated (with europium and manganese) forms. Excitation was by means of the radioactive isotopes 45Ca and 35S, which were introduced both separately and together during synthesis. Nonradioactive samples were excited by irradiation with a 9~176 source. The absorbed dose was determined using the ferrous sulfate dosimeter and was 103 rad for the nonradioactive sulfates. The isotopes listed are pure fl-emitters with maximum energies: 45Ca 0.254 MeV, 35S 0.167 MeV, 9~176 0.61 and 2.18 MeV, respectively. The radioactive samples: 45CASO4. Eu, 45CASO4-Mn, 45CASO4" Eu. Mn, Ca3SSO4 �9 Eu, CaZSSO4 �9 Mn, Ca3~SO4 - Eu- 1Vln, 45Ca35SO4 - Eu, 45Ca35SOr �9 Mn, 45Ca35SO4 �9 Eu. Mn, Sr35SO4 �9 Eu, Ba35SO4, Ba35SO4 �9 Eu and nonradioactive samples of the unactivated sulfates of strontium and barium were synthesized in sealed quartz tubes by growing them from solution in a sodium chloride melt. The TL curves of these substances were obtained on standard equipment using the generally accepted

Elaboration et caracterisation de monocristaux de V 2O 3 par transport en phase vapeur

Single crystals of V 2O 3 are obtained by HCl or TeCl 4 chemical transport method in sealed quartz tubes with temperature gradients of 1050–930°C and 990–900°C respectively. The hexagonal prims are 5 mm long and 1 or 2 mm wide. Both kinds of crystals are characterized by sharp insulator-metal transition at 156 and 137 K respectively, they present a large hysteresis. The sharp decrease in resistivity with increasing temperature is of the order of 10 8 at the transition.

Croissance épitaxique des composés II–VI en phase vapeur

A method is described for growing II–VI compounds by vacuum sublimation. The process takes place in a sealed quartz tube which has three parts: a container in the main part continued at the top by a capillary tube, and having at the opposite side a tube of a few cm in length. The capillary aims to perform the stoichiometry of the charge in order to adjust the pressure to its minima value. For a given temperature gradient, the transport velocity is then of the greatest value (about (0.5 mm h -1). A seed is put in the lowest tube in order to prevent spurious nucleation. The system is moved with a constant speed in a vertical furnace. Crystals of several cm 3 of ZnTe, CdS, ZnSe and ZnS have been grown by this method.

Hollow crystals of ZnS obtained by the pulling sealed tube method

Hollow single crystals of ZnS were obtained by pulling, at a rate of 2.8–3.0 mm/hr, a sealed quartz tube charged with ZnS powder (99.999%) and filled with Ar-H 2 gases (95:5 in volume) at a pressure of 160–170 mm Hg at 80 °C. A ring made of fire brick of an appropriate size was attached to the tube causing an unusual temperature distribution in the furnace, which was necessary to grow hollow single crystals of an optimum size for X-ray examination. The maximum temperature of the furnace was 1280 °C and the duration of pulling was more than 20 hr. The growth of temperature of the hollow crystals was estimated to be less than 1190 °C. The polytypical crystal structures determined by X-ray method differ from part to part in the same single crystal and they are not the only 2H, but also many other polytypical structures, some of which have the number 1 in Zhdanov symbols.

Zur züchtung von ZnSe-einkristallen durch chemische transportreaktion

Cubic ZnSe single crystals have been grown without seeds by chemical transport in a sealed quartz tube by a special method, which is described. Transport reagant was I 2. The used ZnSe and I 2 were prepared from “ultrapure” materials by vacuum-sublimation. The temperature of the surface of the growing crystals was at 780 °C, the temperature of the seed was at 850 °C (hence Δ T ≅ 70 °C). Length of the crystals = 20 mm, diameter = 10 mm. The crystals were yellow up to orange and ideally transparent. The free grown ends of the crystals show plane and smooth (100)- and (111)-faces.

Magnetic properties of transition metal-rare-earth chalcogenide spinels

Three transition metal-rare-earth chalcogenide spinels have been prepared by high-temperature solid-state reaction in evacuated sealed quartz tubes, and their magnetic susceptibilities determined as a function of temperature with Faraday apparatus. Results indicate that MnYb 2S 4 and MnYb 2Se 4 both contain divalent Mn and trivalent Yb, but FeYb 2S 4 appears to contain trivalent Fe and trivalent Yb. This may be explained on the basis of delocalization of one of the 3 d electrons of Fe, which might be expected to make the compound an electrical conductor. Conductivity has indeed been experimentally observed in this compound, while the two Mn compounds are insulators. None of the data indicates long-range magnetic order in any of the compounds.

The preparation and growth of single crystals of some ternary sulphides

The application of the Stockbarger technique to the growth of single crystals of ternary sulphides has been investigated. Single crystals of CdIn 2S 4, ZnIn 2S 4 and CdGa 2S 4 have been prepared, both from the constituent binary sulphides and the basic elements. While the latter yields crystals more easily, the former shows a lower incidence of fracture of the sealed quartz tubes.

Diffusion from a Plane, Finite Source into a Second Phase with Special Reference to Oxide‐Film Diffusion Sources on Silicon

A model is set up for the diffusion from a source of finite thickness into an adjacent second phase of semi‐infinite extent. With the principal assumption of no diffusion in or out of the system, a solution is obtained for the diffusion profile in the second phase. It is also assumed that the diffusion coefficients are independent of concentration, but segregation at the inter‐phase boundary is taken into account and so also, to a first approximation, is the possibility of precipitation or reaction at the interface. The model predicts a change in the profile from an ERFC to Gaussian shape depending on whether the diffusion length in the source is much less than or much greater than its thickness, i.e., as the diffusion time increases.The theoretical predictions of the model are compared to tracer diffusion results from phosphorus doped anodic oxide sources on silicon. These experiments were carried out with unprotected (no undoped film covering the source) oxide sources in a sealed quartz tube. Thus the phosphorus initially lost by out‐diffusion could not escape from the system altogether, and it is shown that these conditions approximated the boundary condition of no out diffusion. The diffusion results obtained in this way are in agreement with the model.

Die synthese von boraziten mit hilfe chemischer transportreaktionen

A new method of preparing boracites (Me 3B 7O 13 X, Me = a bivalent metal, X = Cl, Br or I) is described. The process takes place in sealed quartz tubes with the aid of chemical transport reactions and permitted the preparation of a large number of boracites, among which the Cr-Br-, Cr-I-, Cu-Cl- and Cu-Br-boracites were not reported before. In most cases, single crystals were obtained. The transport of MeO to the growing boracite crystal can be achieved by the reaction MeO + 2 H X( g) = Me X 2( g) + H 2O( g) or MeO + X 2( g) = Me X 2( g) + 0.5 O 2 and that of CuO via the cuprous halides. B 2O 3 is preferably transported via a liquid film to the growing crystal. At high H X- and H 2O pressure, we observed the formation of boracite, based on transport of B 2O 3 via the gas phase. Thermodynamical estimations of the situation of the transport reaction equilibria of MeO and B 2O 3 are made. The results are discussed with respect to the observed crystallization properties of the different boracites. By means of transport of MeO and B 2O 3 via the gas phase, several known and some new transition metal borates were obtained. In an orienting experiment, Mg-Cl-boracite was prepared at about 150 to 180°C by transport reactions in aqueous solution. The lattice parameters and α-β-transition temperatures of all prepared boracites were determined. On Co-J-boracite, an alexandrite-effect is observed. The Fe-Cl-, Fe-Br-, Ni-Cl-, Ni-Br-, Ni-J, and Cu-Br-boracites show thermochroism.

Magnetization, Resonance, and Optical Properties of the Ferromagnet CrI3

CrI3, noteworthy as one of the few insulating ferromagnets, is one of a series of presumably isomorphous compounds (CrCl3, CrBr3, and CrI3) which show similar or closely related magnetic ordering. CrI3 samples containing some single crystals (plates a few square millimeters in area) were made by reacting chromium metal and iodine in a sealed quartz tube. Magnetization measurements of the powder were made by Williams and Sherwood at several fields up to 15 300 Oe over the range 1.5° to 300°K. In addition, M (H) was plotted at 4.2°K up to 70 000 Oe. The ferromagnetic Curie temperature is 68°K, and the paramagnetic Curie temperature is 70°K. The low-temperature saturation magnetization is 3.10 μB/Cr+ + +, corresponding to 4πM = 2690 G. The field for ferromagnetic resonance was measured at 86, 91, and 99 Gc/sec. The spectroscopic splitting factor g = 2.07, and the anisotropy field 2K/M = 28.6 kOe at 1.5°K. Optical transmission measurements on CrI3 single crystals showed a very strong absorption band down to a band edge near 10 000 cm−1. The specific magnetic rotations associated with the band edge are almost as large as those observed in the tribromide. Evidence of domain diffraction was seen.

X-ray evidence for CrCO3, VBO3and TiBO2with calcite structure

The borates were prepd. by heating the metal oxides, halides, and H3BO3 in a sealed quartz tube. Structures were deduced from x-ray powder diagrams.

Some Comments on Thermal Etching of Silicon Surfaces Treated in Sealed Quartz Tubes

not Available.

The Preparation and Properties of Some II – V Semiconducting Compounds

The methods of purification and single crystal growth of six II – V semiconducting compounds are discussed and crystallographic data are presented. The six compounds, representing three stoichiometries, are , , , , , and . The compounds are thermally dissociated in the vapor phase, and the solid‐vapor equilibria of four of the compounds has been measured. Because of the thermal instability, crystal pulling was carried out in sealed quartz tubes employing magnetic suspension of the seed. Through purification of the elements and single crystal growth, high purity was attained in most of the compounds. The highest purity is represented in with an electron carrier concentration of .

Electrical Properties of Mercury Telluride

Polycrystalline HgTe, as prepared in sealed quartz tubes, was found to be $p$ type with acceptor concentrations of ${10}^{18}$-${10}^{19}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ and band gap \ensuremath{\sim}0.02 ev. Diffusion of zinc and copper into samples indicates that the former is a donor impurity, the latter an acceptor impurity. Measurements of resistivity and Hall effect extended to liquid hydrogen temperature reveal a marked magneto-Hall effect. The Hall coefficient changes sign at temperatures as low as 20\ifmmode^\circ\else\textdegree\fi{}K. Some measurements of thermoelectric power and thermal conductivity are also given.